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Brown shield bug

  • Close up photograph of  an adult Brown shield bug resting on plant material - image copyright J. Wessels
    Close up photograph of an adult Brown shield bug resting on plant material - image copyright J. Wessels
  • Close up photograph of two Brown shield bug egg rafts anchored on plant material - image copyright J. Wessels
    Close up photograph of two Brown shield bug egg rafts anchored on plant material - image copyright J. Wessels
Scientific nameDictyotus caenosus. Also known as the brown stink bug (BSB) and, less frequently, the brown ground bug.
Description

BSB adults are shield shaped and are matt mid brown (i.e. are not glossy). They are noticeably smaller than the green vegetable bug (GVB), being only 8 mm long. Newly hatched nymphs are orange with black markings and are very similar to newly hatched nymphs of many other shield bugs. BSB lays eggs in either small twin row or small irregular rafts containing 10-16 eggs. The eggs are pale cream and similar in shape to GVB eggs. Larger nymphs have dark brown (sometimes almost black) heads and thoraxes, and a pale brown abdomen with transverse dark brown and pale (almost white) markings at its centre. There is also a transverse pale band at the front of the abdomen.

Similar to

Adults may be confused with those of the glossy shield bug , which is slightly larger and is a predatory species. Nymphs of this species are completely different to BSB nymphs.

Crops attacked

BSB are known to feed on soybeans, mungbeans, navy beans, cotton and azuki beans.

Pest status: Minor, widespread and irregular. However, sometimes reported in large numbers in soybeans and other summer pulses in the western Darling Downs of Queensland, and in northwest New South Wales.

Life cycle

BSB typically invade summer legumes at flowering and commence feeding and egg laying. Nymphs usually reach a damaging size during mid to late podfill. There are five nymphal stages. Usually only one BSB generation develops per summer legume crop but more than one generation is possible if temperatures are high.

Risk period

BSB typically invade summer legumes at flowering, but are primarily pod feeders with a preference for pods with well-developed seeds. Summer legumes remain at risk until pods are too hard to damage (i.e. very close to harvest). Damaging populations are typically highest in late summer crops during late podfill (when nymphs have reached or are near adulthood).

Damage

Damage is similar to that caused by GVB: early damage can cause potential yield loss, with damage reducing the quality of harvested seeds. BSB adults damage only 20% as many seeds as GVB.

Action level: Populations of podsucking bugs other than GVB are converted to GVB equivalents, and decisions made accordingly based on the GVB thresholds. Adult BSB are equivalent to 0.2 of a GVB. Nymphs are less damaging than adults.

Monitoring

Beat sheeting is the preferred sampling method. Sample crops in the early to mid morning when bugs are more likely to be at the top of the crop. Look for the distinctive egg rafts, which indicate the presence of BSB.

Control

Chemical control: No insecticides are specifically registered against BSB in Australia. However, BSB are likely to be controlled by pesticides targeting green vegetable bug. For current chemical control options see Pest Genie or APVMA.

Cultural control: Where possible avoid sequential plantings of summer legumes, as this allows successive generations of podsucking bugs to build up. Spring plantings are at lesser risk than summer planted crops.

Conservation of natural enemies: Spiders, ants, and predatory bugs are major predators of BSB, particularly of eggs and young nymphs with mortality of these stages sometimes exceeding 90%. Eggs may be parasitised by the tiny wasp Trissolcus basalis.

Distribution

Native to Australia but introduced to New Zealand and New Caledonia. Reported from Queensland and New South Wales but most likely more widely spread.

Further information

  • Pests of Field Crops and Pastures: Identification and Control. Editor: PT Bailey